Iran and the U.S. conducted a prisoner exchange Saturday that saw a detained Princeton scholar released for an Iranian scientist held by America, marking a rare diplomatic breakthrough between Tehran and Washington after months of tensions.

In a trade conducted in Zurich, Switzerland, Iranian officials handed over Chinese-American graduate student Xiyue Wang, detained in Tehran since 2016, for scientist Massoud Soleimani, who had faced a federal trial in Georgia.

While the exchange represents a rare win for both countries, it comes as Iran still faces crushing American sanctions and the aftermath of nationwide protests that reportedly saw over 200 people killed. Meanwhile, Western detainees from the U.S. and elsewhere remain held by Tehran. They are likely to be used as bargaining chips for future negotiations amid Iran’s unraveling nuclear deal with world powers.

Wang’s release had been rumored over recent days, with one lawyer involved in his case tweeting out a Bible verse about an angel freeing the apostle Peter just hours before Iranian Foreign Minister Mohammad Javad Zarif broke the news in his own tweet.

“Glad that Professor Massoud Soleimani and Mr. Xiyue Wang will be joining their families shortly,” Zarif wrote. “Many thanks to all engaged, particularly the Swiss government.”

President Donald Trump shortly after acknowledged Wang was free in a statement from the White House, saying the Princeton scholar would be “returning to the United States.”

“Mr. Wang had been held under the pretense of espionage since August 2016,” Trump said. “We thank our Swiss partners for their assistance in negotiating Mr. Wang’s release with Iran.”

The Swiss Embassy in Tehran looks out for America’s interests in the country as the U.S. Embassy there has been closed since the 1979 student takeover and 444-day hostage crisis.

Brian Hook, the U.S. special representative for Iran, accompanied the Iranian scientist Soleimani to Switzerland to make the exchange and will return with Wang, according to a U.S. official who spoke on condition of anonymity as the information had yet to be released. Hook and Wang were en route to Landstuhl hospital at Ramstein Air Base in Germany where Wang will be examined by doctors, the official said. Hook is expected to return to the U.S. from Germany alone, as Wang is expected to be evaluated for several days.

Although Hook was present for the swap, the official said Trump’s national security adviser Robert O’Brien played the lead role in the negotiations dating from his time as the special representative for hostage affairs at the State Department.

Iran’s state-run IRNA news agency later reported that Soleimani was with Iranian officials in Switzerland. Soleimani was expected to return to Iran in the coming hours. Zarif later posted pictures of himself on Twitter with Soleimani in front of an Iranian government jet and later with the two talking on board.

Wang was sentenced to 10 years in prison in Iran for allegedly “infiltrating” the country and sending confidential material abroad. His family and Princeton University strongly denied the claims. Wang was arrested while conducting research on the Qajar dynasty that once ruled Iran for his doctorate in late 19th and early 20th century Eurasian history, according to Princeton.

Hua Qu, the wife of Xiyue Wang, released a statement saying “our family is complete once again.”

“Our son Shaofan and I have waited three long years for this day and it’s hard to express in words how excited we are to be reunited with Xiyue,” she said. “We are thankful to everyone who helped make this happen.”

Princeton University spokesman Ben Chang said the school was aware of Wang’s release.

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